1. Field of the Invention
This invention relates to an electronic wristwatch, and more particularly, to a crystal wristwatch with an electronic sound emitter device which vibrates a small size piezo-electric sound converter element by a signal from a frequency standard source of the wristwatch.
2. Prior Art
Prior art devices disclose a wristwatch with an electronic sound emitter device which requires a high voltage in order to vibrate a piezo-electric sound converter element. The maximum voltage which can be obtained from a small size battery suitable for placing in a wristwatch is approximately three volts. Usually, in order to increase voltage requirements, a transformer is used. However, it has been very difficult to produce a transformer small enough to be conveniently installed in a wristwatch. Another prior art method of operating a piezo-electric sound converter element is to use a relaxation oscillator or a blocking oscillator. Both the blocking oscillator and relaxation oscillator dissipate a considerable amount of power, and have a physical size not suitable for a wristwatch. Hence production of an electronic wristwatch with an electronic sound emitter device has not been achieved.
Recently a mechanical wristwatch combined with an electronic sound emitting divce has been manufactured. However, it lacks a compact arrangement whereby the sound emitting device and the mechanical part could share the electronic circuit. To the contrary the electronic device is merely placed physically into the mechanical watch. Consequently it does not appear as a welldesigned wristwatch.
In recent years, a crystal wristwatch with a small sized, low power C-MOS (Complimentary Metal Oxide Semiconductor) circuit has been on the market, and since that time production of crystal wristwatches with piezo-electric sound emitter device has been desired.
In the case of the above-mentioned wristwatch, the sound emitter driving circuit comprising C-MOS transistors are used to set a low frequency signal by dividing the oscillator signal from the crystal oscillator by the use of multi-stage frequency divider. However, one of the difficulties encountered in this crystal wristwatch was to emit alarm sound loud enough to be heard by human ear.
Furthermore, the mechanical resonance frequency of said piezo-electric sound converter element is limited by the size of the wristwatch and its operational range of the frequency will be from 1K Hz to 8K Hz. In a case where the series divided frequency signal obtained from the multi-stage frequency divider is directly used, the frequency of the most effective alarm sound to the human ear is below 1K Hz. Therefore, if the frequency of the sound from 1K Hz to 8K Hz of said wristwatch is used, the alarm sound of said wristwatch can hardly be heard by the human ear except at its beginning.